Observations on egg-laying behaviour of the banana weevil,Cosmopolites sordidus (Germar)

Banana weevil females laid on an average 2.7 eggs/week in rhizome material and 0.7 eggs/week in pseudostem material in the laboratory. At extremely high weevil population densities the egg-laying activity declined. Under controlled field conditions 0.7 eggs/week were laid in banana suckers and 1.3 eggs/week in stumps of harvested suckers. 25% of the weevil stages found in suckers in the field were eggs of which 78% were laid in the rhizome and 22% in the pseudostem base. The majority of eggs was deposited in the crown area of the rhizome followed by the remaining surface area of the rhizome, the walls of abandoned larval tunnels in rhizome and pseudostem and the leaf sheaths. 58% of the eggs found were considered accessible to egg predators.     

Beauveria bassiana (Balsamo) Vuillemin as an endophyte in tissue culture banana (Musa spp.)

Beauveria bassiana is considered a virulent pathogen against the banana weevil Cosmopolites sordidus. However, current field application techniques for effective control against this pest remain a limitation and an alternative method for effective field application needs to be investigated. Three screenhouse experiments were conducted to determine the ability of B. bassiana to form an endophytic relationship with tissue culture banana (Musa spp.) plants and to evaluate the plants for possible harmful effects resulting from this relationship. Three Ugandan strains of B. bassiana (G41, S204 and WA) were applied by dipping the roots and rhizome in a conidial suspension, by injecting a conidial suspension into the plant rhizome and by growing the plants in sterile soil mixed with B. bassiana-colonized rice substrate. Four weeks after inoculation, plant growth parameters were determined and plant tissue colonization assessed through re-isolation of B. bassiana. All B. bassiana strains were able to colonize banana plant roots, rhizomes and pseudostem bases. Dipping plants in a conidial suspension achieved the highest colonization with no negative effect on plant growth or survival. Beauveria bassiana strain G41 was the best colonizer (up to 68%, 79% and 41% in roots, rhizome and pseudostem base, respectively) when plants were dipped. This study demonstrated that, depending on strain and inoculation method, B. bassiana can form an endophytic relationship with tissue culture banana plants, causing no harmful effects and might provide an alternative method for biological control of C. sordidus.     

How brood influences caste aggregation patterns in the dimorphic ant species Pheidole pallidula

Spatial distribution of ant workers and, notably their aggregation/segregation behaviour, is a key-element of the colony social organization contributing to the efficiency of task performance and division of labour. In polymorphic species, specialized worker castes notably differ in their intrinsic aggregation behaviour. In this context, knowing the preponderant role of minors in brood care, we investigate how a stimulus such as brood can influence the spatial patterns of Pheidole pallidula worker castes. In a homogeneous area without brood, it was shown that minors display only a low level of aggregation while majors form large clusters in the central area. Here we find out that these aggregation patterns of both minors and majors can be deeply influenced by the presence of brood. For minors, it nucleates or enhances the formation of a large stable cluster. Such high sensitivity of minors to brood stimuli fits well with their role as main brood tenders in the colony. For majors, interattraction between individuals still remains the prevailing aggregation factor while brood strongly influences the localisation of their cluster. We discuss how the balance between interattraction and sensitivity to environmental stimuli determines the mobility of each worker castes and, consequently, the availability of minors and majors to participate in everyday colony tasks. Moreover, we will evoke the functional value of majors’ cluster location close to the brood, namely with respect to social regulation of the colony caste ratio. Received 30 May 2005; revised 11 January 2006; accepted 13 January 2006.     

Unadapted behaviour of native,dominant ant species during the colonization of an aggressive,invasive ant

Among the factors driving the invasive success of non-indigenous species, the “escape opportunity” or “enemy release” hypothesis argues that an invader’s success may result partly from less resistance from the new competitors found in its introduced range. In this study, we examined competitive interactions between the little fire ant Wasmannia auropunctata (Roger) and ant species of the genus Pheidole in places where both are native (French Guiana) and in places where only species of Pheidole are native (New Caledonia). The experimental introduction of W. auropunctata at food resources monopolized by the Pheidole species induced the recruitment of major workers only for the Guianian Pheidole species, which were very effective at killing Wasmannia competitors. In contrast, an overall decrease in the number of Pheidole workers and no recruitment of major workers were observed for the New Caledonian species, although the latter were the only ones able to kill the Wasmannia workers. These results emphasize the inappropriate response of native dominant New Caledonian species to W. auropunctata and, thus, the importance of enemy recognition and specification in the organization of ant communities. This factor could explain how invasive animal species, particularly ants, may be able to successfully invade species-rich communities.     

Territory defense by the ant Azteca trigona: maintenance of an arboreal ant mosaic

Mosaics of exclusive foraging territories, produced by intra-and interspecific competition, are commonly reported from arboreal ant communities throughout the tropics and appear to represent a recurring feature of community organization. This paper documents an ant mosaic within mangrove forests of Panama and examines the behavioral mechanisms by which one of the common species, Azteca trigona, maintains its territories. Most of the mangrove canopy is occupied by mutually exclusive territories of the ants A. trigona, A. velox, A. instabilis, and Crematogaster brevispinosa. When foraging workers of A. trigona detect workers of these territorial species, they organize an alarm recruitment response using pheromonal and tactile displays. Nestmates are attracted over short distances by an alarm pheromone originating in the pygidial gland and over longer distances by a trail pheromone produced by the Pavan's gland. Recruits are simultaneously alerted by a tactile display. No evidence was found for chemical marking of the territory. Major workers are proportionally more abundant at territory borders than on foraging trails in the interior of the colony. The mechanisms of territory defense in A. trigona are remarkably similar to those of ecologically analogous ants in the Old World tropics.     

Volatile components of banana pseudostem of a cultivar susceptible to the banana weevil

Volatiles from banana (‘githumo’'cultivar) pseudostem were trapped using porapak S. The trapped volatiles were desorbed from porapak columns by elution with dichloromethane and analysed using GC and GC-MS. The volatile compounds identified included -pinene, β-pinene, β-myrcene, limonene, -cubebene, -copaene, -cedrene, β-caryophyllene and -humulene.     

Effects of two pheromone trap densities against banana weevil, Cosmopolites sordidus, populations and their impact on plant damage in Uganda

Abstract:  An on-farm study to evaluate the effect of pheromone trap density on the population of the banana weevil, Cosmopolites sordidus (Germar) (Col., Curculionidae) was conducted in Masaka district, Uganda. The pheromone used was Cosmolure+, a commercially available weevil aggregation pheromone. Forty-two farms were assigned to one of three treatments: 0, 4 and 8 pheromone traps/ha. Pheromone lures were changed monthly at which time the traps were moved to a different location within the stand. Adult weevil population densities were estimated by using mark and recapture methodology at 0, 6, 12, 18 and 21 months, while damage to the banana corm was assessed at 0, 3, 6, 12, 18 and 21 months since the start of the experiment. Pheromone trap captures were generally low: about 10 weevils per trap per month. There were no significant differences in mean catches of C. sordidus per trap per month except for February 2002 when doubling the pheromone trap density decreased weevil catches. Although not significant, decreased efficiency was also the trend in higher trap densities over all the data sets. Doubling the number of traps increased the number of weevils caught per hectare per month from 0.4 to 0.6%. There was no significant difference in plant damage between the pheromone treatments in low- compared with high-trap densities. There were generally no significant differences in weevil populations and plant damage between pheromone-treated and control farms. Possible reasons for the low-trap efficacy in this study are discussed.     

The use of aggregation pheromone to enhance dissemination of Beauveria bassiana for the control of the banana weevil in Uganda

Candidate strains of Beauveria bassiana were identified for use in integrated pest management of the banana weevil Cosmopolites sordidus. Horizontal field transmission of B. bassiana between banana weevils using different delivery systems, including aggregation pheromones, was investigated. We observed that infected weevils could transmit the fungal pathogen to healthy individuals. Most dead weevils (52%) due to B. bassiana infection were found at the base of banana plants in the leaf sheath or in the soil near banana plants. Significantly more weevils died from the pathogen in plots where B. bassiana was applied in combination with the pheromone than where it was applied alone. Our data demonstrate that C. sordidus aggregation pheromone can be a valuable tool to enhance the dissemination of B. bassiana for the control of C. sordidus.     

Polynesian ant (Hymenoptera: Formicidae) species richness and distribution: a regional survey

Thirteen Polynesian islands, including five true atolls, an uplifted atoll, and seven high volcanic islands of varying ages, were surveyed for ants by hand collecting techniques. Ten of the thirteen islands had been surveyed previously, and more and species were found in the present survey than were known from all earlier surveys combined, with two exception (Ducie Atoll and Easter Island).This represents the first report of the Argentine ant, Linepithema humile Mayr, from Easter Island. L. humile is a very successful pest species which has only recently invaded Easter Island, and is now very abundant and widespread, occurring at 16 of the 17 sample sites scattered across the island. The introduction of this species is almost certainly responsible for the apparent decline in species richness on Easter Island.In general, more species were present on high islands than atolls of a similar size, and elevation was significant while log (area) and latitude were not in a multiple linear regression with ant species number as the dependent variable. Not enough time was spent on the islands to survey their ant faunas completely, and extrapolations from species effort curves and jackknife estimators of earlier, thorough surverys for ants in the society Islands suggest that only about 50% of the total species were collected in the present survey, at least on the high islands. My collections were probably more complete on the atolls. The increase in species numbers from the present survey relative to known species richnesses (particularly when a large fraction of the species actually present were probably not included in the present survey) supports the hypothesis that remote Polynesian islands are not as depauperate in terms of ant species numbers as previously thought.     

Experimental small-scale grassland fragmentation alters competitive interactions among ant species

Different species may respond differently to habitat fragmentation. Theory predicts that abundant generalist species should be less affected by fragmentation than specialist species. In ant communities, the most abundant species is often behaviourally dominant. Thus, habitat fragmentation could alter competitive interactions between the dominant ant species and the other species. We tested this hypothesis in a long-term grassland fragmentation experiment. Fragments of different size (20.25 and 2.25 m²) were isolated by a 5-m wide strip of frequently mown vegetation. Control plots were situated in adjacent undisturbed grassland. Ant density and species composition were assessed 3 and 6 years after initiation of the experimental fragmentation. The effect of the dominant ant species on the resource use of the other species was examined at natural sugar resources (aphids and extrafloral nectaries) and at artificial sugar baits. Lasius paralienus was the most abundant ant species (72% of nests) in the grasslands examined. Species richness and forager density in the other species decreased with increasing density of L. paralienus in fragments but not in control plots. The overall forager density of the other species was positively related to their habitat niche overlap with L. paralienus. The density of foragers of the other species at sugar resources was not affected by L. paralienus forager density. The experimental fragmentation resulted in an increase in natural sugar resources in fragments. This may have reduced the intensity of interspecific competition for sugar resources. Our study shows that the grassland fragmentation altered interactions between the dominant L. paralienus and the other ant species.Electronic Supplementary Material Supplementary material is available for this article at     

Prey availability and eclosion-help of callow workers in the formicine ant Camponotus mus

Summary In the ant Camponotus mus the eclosion of imagines from the cocoons was shown to be controlled by nurse workers, which broke the cocoons and assisted the callows to energe. Short-term colony prey deprivation modified the eclosion-help behavior resulting in a delay in cocoon opening times. During long-term prey deprivation, no new cocoons were spun; the starved larvae grew and pupated when prey was again available. These findings as a colony strategy adapted to the changing condition of prey availabitity in a temperate habitat are discussed.     

Response of two Lathyrus species to infestation by the pea weevil Bruchus pisorum L. (Coleoptera: Bruchidae)

Oviposition behavior and larval mortality of the pea weevil, Bruchus pisorum L. on Lathyrus tingitanus L. and Lathyrus sativus L. were studied to determine the mechanisms by which these plant species resist pea weevil attack. Female weevils caged on pods of these species oviposited at a reduced rate compared to those caged on pods of pea, Pisum sativum L. Females kept in vials in the laboratory and given a choice between L. sativus pods and pea pods oviposited at a higher rate on pea and the glass vial than on L. sativus. Two to three days following oviposition, L. tingitanus pods developed callus tissue growth beneath the eggs. These growths later covered much of the pod. L. sativus pods exhibited a similar response to hatching larvae. Pea weevil larvae attempting to penetrate pods of both species died. Larvae placed inside L. sativus pods established in seeds and had no greater mortality after 72 h than those placed inside pea pods. Identified defenses in lathyrus against pea weevil attack consist of antibiosis as well as antixenosis. These resistance mechanisms are located in the pod.

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Résumé Les espèces de Lathyrus sont indemnés d'attaques de la bruche du pois, Bruchus pisorum, bien que le pollen de deux membres de ce genre ait induit, après ingestion, l'ovogenèse des femelles. La ponte et la mortalité larvaire de B. pisorum sur L. tingitanus et L. sativus (Leguminosae) ont été examinées pour déterminer les mécanismes permetant à ces espèces de résister à l'attaque de cette bruche. Des femelles aux ovaires développés ont été mises en cage en serre, avec des gousses de chacune des deux espèces de Lathyrus et de Pisum sativum; les femelles ont pondu beaucoup moins sur Lathyrus que sur Pisum. Au laboratoire, des femelles aptes à pondre, placées dans des bocaux avec des gousses de même taille de L. sativus et P. sativus, ont pondu sur le pois et le bocal que sur L. sativus.Deux à 3 jours après contamination par les oeufs de bruche, les gousses de L. tingitanus forment des cals sous les oeufs. Ces excroissances s'étendent de telle sorte que la majorité de la gousse en est recouverte quelques jours plus tard; les gousses de L. sativus présentent une réponse semblable mais plus localisée. La croissance du cal se produit en réponse à l'éclosion plutôt qu'à la ponte, car aucune n'a été observée sous les oeufs qui n'ont pas éclos, et aucune s'étend au-delà des zones immédiatement sous les oeufs éclos. Les larves de B. pisorum tentant de pénétrer dans les gousses des 2 espèces meurent, tandis que des larves placées à l'intérieur des gouses de L. sativus n'ont pas présenté une mortalité supérieure dans les graines au bout de 72 h à celle des larves placées à l'intérieur des gousses de pois. On peut envisager que la reconnaissance de stimuli dissuasifs par les femelles de bruches ait pu évoluer en réponse à la présence de mécanismes de défense de la gousse.

     

Complexity of species conservation in managed habitats: interaction betweenMaculinea butterflies and their ant hosts

Europe's five species ofMaculinea butterfly are examples of endangered species adapted to live in traditional, cultural landscapes. All are threatened with extinction in Western Europe because of recent changes in land use. This is illustrated by an historical account of the extinction of the BritishMaculinea arion populations, despite many conservation attempts. It is shown how the failures proved to be due to ignorance of the key factor forM. arion, its specialization on a single ant host,Myrmica sabuleti. A brief account is given of research that shows how each of the five species is similarly dependent upon a separate hostMyrmica ant species and how each has an interesting and rare specific parasitoid. Steps for the practical conservation of existingMaculinea populations including the obligation, under the Bern Convention, to re-establish nationally extinct species are outlined. The procedure and problems involved in re-establishment are illustrated with reference to the successful programme forM. arion in Britain. The best way of ensuring robust populations ofMaculinea butterflies is to manage habitats to optimize the density and distribution of the required species ofMyrmica host and, secondarily, the distribution of the larval food plant. The value of single species conservation in cultural habitats is discussed. It is concluded that this is possible to achieve and that other rare organisms also often benefit, but only when conservation measures are based on the results of detailed autecological research.     

Biological control of black vine weevil Otiorhynchus sulcatus in Ireland using Heterorhabditis megidis

Heterorhabditis megidis (UK211) was applied against black vine weevil (BVW, Otiorhynchus sulcatus) in potted plants in a polyethylene (2002) or glasshouse (2003) and in field planted strawberries (2003). Both potted and field strawberries were artificially infested with BVW larvae. In a 2002 pot planting in the polyethylene house, a single drench application of 25,000 H. megidis infective juveniles per plant in 50 ml of water in mid September, reduced the number of BVW larvae to 1.8/20 plants. A second application in early October gave a reduction of 0.2/20 plants and in the third application, the following March no live weevils were recovered, compared to the control which had 8.2 larvae/20 plants. In a 2003 pot planting in a glasshouse, similar treatments gave a reduction of 5.2, 5.4 and 0.8 larvae/20 plants, respectively, compared to the control where 26.2 larvae/20 plants were recovered. In an artificially, BVW infested field trial, similar treatments gave a reduction to 2.2 larvae/20 plants in the single September treatment, and 2 larvae/20 plants in the single October treatment. The double (September and October) application reduced BVW larvae further to 1.6/20 plants and the triple (September, October and April) application to 0.4 larvae/20 plants, compared to the control where four larvae corresponded to every 20 plants. There was, therefore, little difference between the single and double autumn treatments indoors or in the field, and it mattered little whether the single application in the field was made in September or October under the conditions of 2003. Early spring application gave a significant reduction in BVW in each of the three experiments.     

Effects of acidity on the growth of two Euglena species

Our study separates the effects of elevated protons (at pH <3) and elevated metals (Al, Cd, Cu, Fe, Ni, Zn) on the growth of E. mutabilis Schmitz, a pioneering phototroph in acid mine drainage (AMD) and E. gracilis Klebs, a closely-related species rarely found in severely AMD-impacted sites. Both species were acid tolerant, growing optimally at pH 2.5–7. At pH values typical of AMD (pH 2.5–4) in the absence of elevated metals, E. gracilis outcompeted E. mutabilis (growth rates of 1.0 and 0.8 div d^–1, respectively). Relative metal toxicities were evaluated based on the Effective Exposure causing 50% growth reduction (= EE50). With total metal additions similar to AMD levels, E. mutabilis demonstrated significantly greater tolerance to all metals, except Cu. E. gracilis showed two-fold higher tolerance to Cu²⁺ than E. mutabilis (EE50 of 91.6 vs. 45.7 pmol cell^–1). The EE50 for Zn²⁺ was similar for both species (368 pmol cell^–1 for E. gracilis and 423 pmol cell^–1 for E. mutabilis). With Cd and Ni, E. mutabilis tolerated an order of magnitude higher exposure than E. gracilis(EE50 of 1.6 vs. 0.2 pmol Cd²⁺ cell^–1; EE50 of 942 vs. 87 pmol Ni²⁺ cell^–1). Al and Fe were tolerated at high total metal concentrations (up to 100 mM) by E. mutabilis, but toxicity was evident with E. gracilisat much lower levels. E. mutabilis grew at double the Al³⁺ exposure tolerated by E. gracilis (EE50 of 398 vs. 188 pmol Al³⁺ cell^–1). There was an 18-fold difference in Fe tolerance levels between E. mutabilis and E. gracilis with EE50s of 8773 and 502 pmol Fe²⁺ cell^–1, respectively. We conclude that differential metal tolerance, particularly to Fe²⁺, accounts for the mutually exclusive distribution of E. gracilis and E. mutabilis in AMD-impacted habitats.     

Distance effects on resource profitability and recruitment in the giant tropical ant,Paraponera clavata

Summary We examine how cost and benefit components of resource profitability affect recruitment in the giant tropical ant, Paraponera clavata. To vary resource profitability, we changed the quantity of artificial nectar baits presented to foragers and the distance of nectar baits from the nest. Both distance to and amount of resource affected quantitative aspects of recruitment. At increased distances foragers were less likely to recruit, and fewer workers were recruited to the resource area. The amount of nectar affected the tendency of foragers to recruit, but had no effect on the number of ants recruited. Variation in resource distance was also associated with qualitative changes in recruitment strategy. Foragers at distant sites recruited from the canopy rather than from the nest, and often transferred nectar to other workers for transport to the nest. Nectar transfer and extra-nidal recruitment significantly reduced the time required for resource collection. It may also have increased the ability of workers to specialize in specific foraging tasks. A portion of the colony's foraging force specialized spatially by remaining in distant foraging areas without returning to the nest. The flexible recruitment system of P. clavata increases colonial net energetic gain rates by concentrating foraging effort on resources yielding the highest net energetic rewards, and increases the competitive abilities of individual colonies at resource sites by decreasing collection times.     

Interference and exploitation competition of three nectar-thieving invasive ant species

Summary. Plant and insect exudates are known to play a key role in structuring tropical ant communities, but less is known about the utilization of these resources in communities dominated by invasive ants. Invasive ants are thought to require large amounts of carbohydrates such as honeydew or nectar to maintain their high abundances. Invasive ants that consume floral nectar may compete with legitimate floral visitors through interference or exploitation competition. I compared the nectar-thieving behavior of three widespread invasive ant species: long-legged ants (Anoplolepis gracilipes), Argentine ants (Linepithema humile), and big-headed ants (Pheidole megacephala) in inflorescences of the native Hawaiian ‘ōhi’a tree, an important food source for native fauna. A. gracilipes was least likely to leave inflorescences unvisited and visited inflorescences in higher numbers than both L. humile and P. megacephala. A. gracilipes and L. humile visited more flowers in an inflorescence and were less likely to retreat from a flower with a competitor than P. megacephala. A. gracilipes was able to take 5.5 and 11.3 times the amount of nectar than L. humile and P. megacephala, respectively. Thus, A. gracilipes may be effective at both interference and exploitation competition against other nectarivores, L. humile may be effective at interference competition, and P. megacephala may be relatively weak at both types of competition against other nectarivores. Ascertaining the competitive abilities of invasive ants against legitimate floral visitors will be especially important in agricultural and other systems that are nectar or pollinator limited.Received 6 December 2004; revised 13 January 2005; accepted 14 January 2005.     

Allelopathic effects of Cyperus rotundus extract in vitro and ex vitro on banana

Allelopathic effects of Cyperus rotundus on banana ‘Grande Naine’ were studied in vitro as well as ex vitro. To study the allelopathic effects in vitro, the Cyperus extract was added to the multiplication medium during preparation before adjusting the pH. Of the four concentrations, 0.2 and 0.6% decreased the shoot multiplication and shoot length but 1 and 2% extract completely inhibited the shoot multiplication but induced rooting in 50 and 28% shoots, respectively. For the ex vitro studies, the Cyperus extract was added to the hydroponic medium during the hardening of in vitro raised banana plantlets. The extract of 1 and 2% concentrations decreased the shoot and root length, number of leaves and new roots, fresh weight, total chlorophyll and protein. The fluorescence intensity ratio was successively increased resulting in decreased photosynthesis.